Process and an arrangement for the automatic focusing in a photographic enlarging or copying apparatus with a variable enlarging scale

Abstract

According to the focusing process of the invention, in a calibrating stage, a number of focusing positions is stored that are assigned to varying enlarging ratios. In the stage of the automatic focusing, the focusing position for an arbitrary enlarging ratio is computed by interpolation from the stored position values. The arrangement for carrying-out the process comprises memory means for the storing of the position values furnished by the position detectors for the frame holding means and the lens system support, as well as computing means for computing the focusing position for an arbitrary enlarging ratio by means of interpolation from previously stored focusing positions with respect to selected enlarging ratios.

I claim: 
     
       1. A process for the automatic focusing in a photographic enlarging or copying apparatus with a variable enlarging scale, wherein in a calibrating stage, a number of different enlarging ratios are set successively, the corresponding respective focusing positions are found manually and their position values are stored,   in the automatic focusing stage, the focusing position that is assigned to any arbitrary enlarging ratio is computed continuously by interpolation from the number of stored positions, and the determined position is approached in a motor-driven way.   
     
     
       2. A process according to claim 1, wherein the focusing positions are determined by linear interpolation from the number of stored positions. 
     
     
       3. A process according to claim 1, wherein the position values are acquired by means of an incremental sensor with respect to a defined initial position to which a fixed initial value of the sensor is assigned. 
     
     
       4. A process according to claim 3, wherein for the zeroing of the position measuring device, during the startup of the enlarging apparatus, the initial position is reached automatically and/or during the operation, is reached upon the corresponding command from the opearator. 
     
     
       5. A process according to claim 1, wherein a determined focusing position is finally approached in a preferred moving direction. 
     
     
       6. An arrangement for automatically focusing a photographic enlarging or copying apparatus of the type having a movable lens system for providing a variable enlarging scale, said arrangement comprising in combination: a. a base including means for supporting copying material;   b. a projecting head for supporting and lighting a film original to be copied;   c. head support means for supporting the projecting head at a variable distance from the base to provide variable enlarging ratios;   d. first detector means for detecting the position of the projecting head relative to the base and generating a first signal in response thereto;   e. lens support means for supporting a movable lens at a variable distance from the projecting head;   f. a motor drive unit coupled to the lens support means for varying the position of the lens support means and the movable lens supported thereby;   g. second detector means for detecting the position of the lens supporting means relative to the projecting head and generating a second signal in response thereto;   h. a computer electrically coupled to the motor drive unit and to the first and second detector means;   i. a memory electrically coupled to the computer for storing paired values of the first and second signals generated by the first and second detector means, respectively; and   k. control means coupled to the computer and having a calibrating mode and an operating mode, the calibrating mode of said control means allowing a user to manually actuate the motor drive unit to move the lens support means until a focused image of the film original is obtained for a plurality of enlarging ratios, said control means including means for signalling the computer that proper focus has been manually obtained in order to store in the memory the values of the first and second signals generated by the first and second detector means, respectively, for each of the selected plurality of enlarging ratios, the automatic mode of said control means causing the computer to respond to the first signal generated by the first detector means by comparing the first signal to the values of the first signal stored in the memory during the calibrating mode and to compute a calculated focusing position for the lens support means based upon the two closest first signal values stored in the memory by interpolation, the motor drive unit being responsive to the calculated focusing position for automatically moving the lens support means and movable lens to a focused position.   
     
     
       7. An arrangement according to claim 6, wherein the memory and computer are parts of a microprocessor system. 
     
     
       8. An arrangement according to claim 7, wherein the projecting head includes a frame holding means wherein said first and second detecting means convert each position of the frame holding means and of the lens support means into a digital numerical value corresponding to the respective positions thereof. 
     
     
       9. An arrangement according to claim 8, wherein the second detector means has a rotary disk with several reference symbols that is dynamically coupled with the lens support means as well as a detector and counting device for the reference symbols during the rotation of the disk. 
     
     
       10. An arrangement according to claim 9, wherein the reference symbols on the rotary disk are holes or gaps that are arranged in the shape of a circular curve, and the detector and counting device comprises an optical reading device. 
     
     
       11. An arrangement according to claim 8, wherein the rotary disk is fixed on a threaded bush that can be rotated in a plane that is fixed relative to the frame holding means and receives a threaded rod that with one end is fastened at the lens support means. 
     
     
       12. An arrangement according to claim 11, wherein the lens support means can be adjusted relative to the frame holding means that is coupled with the threaded bush. 
     
     
       13. An arrangement according to claim 12, wherein the lens support means includes a stop element, and wherein the threaded bush includes a complimentary stop element, and wherein a predetermined end position of the lens support means is fixed by means of the engagement of the stop element of the lens support means with the complimentary stop element of the threaded bush. 
     
     
       14. An arrangement according to claim 9, wherein the counting direction of the counting device is determined by the polarity of the supply voltage applied to the motor drive unit. 
     
     
       15. A process for the automatic focusing of a photographic enlarging or copying apparatus having a variable enlarging scale, the photographic enlarging or copying apparatus including a movable support for a film original, a movable lens, a support for holding copying material at a copy level, and a motor drive unit for moving the movable lens, the process including the steps of: a. calibrating the apparatus by: (i) positioning the film original at an arbitrary distance from the copy level corresponding to an arbitrary enlarging ratio;   (ii) manually operating the motor drive unit to move the lens to a focused position to form a sharp focused image at the copy level;   (iii) detecting the relative position of the film original and generating a first signal indicative of the arbitrary enlarging ratio;   (iv) detecting the relative position of the lens and generating a second signal indicative of the focused lens position for the aforementioned arbitrary enlarging ratio;   (v) storing the first and second signals in a memory;   (vi) repeating steps i-iv above for different enlarging ratios to build a table of position values in the memory; and     b. automatically focusing the lens for any desired enlarging ratio by performing the steps of: (i) selecting a desired enlarging ratio by positioning the film original at any desired distance from the copy level;   (ii) detecting the relative position of the film original and generating a first signal indicative of the selected enlarging ratio;   (iii) comparing the first signal to the values of the first signal stored in the memory during the calibrating steps (a.i) through (a.v);   (iv) computing a focusing position for the desired enlarging ratio by interpolation from the stored focusing positions corresponding to the stored enlarging ratios defining a range in which the desired enlarging ratio lies; and   (v) operating the motor drive unit under the control of the computed focusing position to automatically move the lens to a focused position.     
     
     
       16. A process according to claim 15, wherein the computed focusing position is determined by linear interpolation from the number of stored focusing positions. 
     
     
       17. A process according to claim 15, wherein the step of detecting the relative position of the lens includes the steps of moving the lens to a defined initial position to which a fixed initial value is assigned and thereafter moving the position of the lens to a focused lens position.